This lecture covers the concept of vector subspaces, focusing on their construction and properties. Starting with the definition of a vector subspace, the instructor explains how to verify if a set is a vector subspace by checking its closure under addition and scalar multiplication. Examples are provided to illustrate different scenarios, such as lines and planes in various dimensions. The lecture also discusses the standard method of constructing vector subspaces through linear combinations of given vectors, emphasizing the importance of understanding the fundamental properties of these subspaces.